1. Field of the Invention
The present invention relates to an evaporative fuel processing system which temporarily stores evaporative fuel generated in a fuel tank, and timely supplies the evaporative fuel to an intake system of an internal combustion engine, and particularly to an evaporative fuel processing system which supplies the evaporative fuel to an internal combustion engine having a turbocharger.
2. Description of the Related Art
In Japanese Utility Model Laid Open Sho 63-162965, an evaporative fuel processing system which supplies evaporative fuel to an intake pipe of an internal combustion engine having a turbocharger is disclosed. In the internal combustion engine having a turbocharger, the intake pressure at a portion downstream of the turbocharger becomes higher than the atmospheric pressure when the turbocharger is operating. Therefore, the evaporative fuel stored in the canister cannot be sufficiently purged to the intake pipe only by a usual purge passage which supplies the evaporative fuel to a portion downstream of the throttle valve.
Therefore, in the system disclosed in Japanese Utility Model Laid Open Sho 63-162965, a connecting passage that has a venturi part and connects an upstream side and a downstream side of the turbocharger (compressor) is mounted on the intake pipe. The purge passage is connected from a canister storing evaporative fuel and the connecting passage, and opens at the venturi part of the connecting passage. This system is configured so that the evaporative fuel may be supplied from the canister to the intake pipe via the connecting passage during operation of the turbocharger, by a negative pressure generated in the venturi part.
However, it is confirmed by experiments that a sufficient negative pressure cannot be obtained only by disposing the venturi part in the connection passage, so that the evaporative fuel is hardly supplied to the intake pipe, or the supplied fuel amount is a very small even if the evaporative fuel can be supplied to the intake pipe.
Further, if the evaporative fuel is supplied to the upstream side of the turbocharger, the intake air and the evaporative fuel is mixed and an evaporative-fuel concentration in the air-fuel mixture may reach a flammability limit. When the evaporative-fuel concentration reaches the flammability limit, there is a possibility that the air-fuel mixture may actually ignite with the heat generated in a compressor and a turbine of the turbocharger.